There are many kinds of cellular mobile radio systems. They may be grouped in various ways depending on various methods of operation. Of particular interest to the present invention is the method used for allotting a radio channel at call set up and handover and the interaction with adjacent or colocated other systems.
Originally cellular mobile radio systems had fixed radio channel reuse plans with fixed allocation of radio channels to base stations and cells. Later on dynamic channel allocation was suggested.
Dynamic Channel Allocation, DCA, has recently been acknowledged to be the only practical way to allocate channels for systems with very small cell sizes. Systems using DCA are for the time being mainly cordless telephone sets and systems, e.g.:
CEPT CT-1: Analog FDMA/FDD 900 MHz. Existing Digital PA1 UK CT-2: FDMA/TDD 800 MHz. Interim '89, CAI-90 PA1 Swedish DCT: Digital Multicarrier (MC) TDMA/TDD 800 MHz 1990 PA1 ETSI DECT: Digital Multicarrier (MC) TDMA/TDD (1.6 GHz) 1992.
The small cells sizes open up possibilities to use very light weight pocket communication sets and at the same time provide extremely high traffic densities on a limited amount of spectrum.
DCA is also shown to be at least twice as freqency efficient as procedures with fixed frequency planning. Especially the TDMA in DCT and DECT gives very quick efficient and elegant procedures for DCA, flexible capacity, call set up and handover, without any need for complicated central control.
Finally DCA adjusts to local conditions and thus opens up new possibilities for shared services. This has been emphasized in a report on Cordless Telephone Product by the European Commission.
A first example is self organizing sharing and market driven capacity for systems performing to the same coexistance specification. The basic advantage is that different systems and system operators and different type of service (e.g. business, telepoint, residential) in a self organizing way, can utilize the same lump of available channels without prior distribution of channels to specific services or base stations. By having C/I limited cell range each service provider can, driven by the market development, increase the capacity by increasing his base station density.
A second example is radio links and a cordless telephone system, DCT, with DCA. The radio links can be fixed or mobile, military or civil. No cordless telephones, CT, are excepted to be in the link beam. The power of the CT is low, max 100 mW. Thus the radio links are not supposed to be interferred by the CT's. The possible interference from the radio links to the CT's will be very local. If the links are military, you do not know where or when or on which exact frequency the interference will occur. A CT, like DCT, with several 1 MHz carriers, will with DCA, adjust locally to the useful carriers. Thus DCT and radio links can coexist well, without detailed prior knowledge of the local situation.
Due to the nature of DCA it is good not to depend on a fixed or special signalling channel e.g. for system information to provide means for a roaming portable to connect to the system. Because that signalling channel has not guaranted protection against interference, and a fixed channel would spoil the concept of free DCA. It is also not good, if a portable which does not know on which channels his wanted system is operating on, pollutes the air in more or less blind trials to get a response from it.
For a PAN European System for instance, a portable may be able to operate on the whole available frequency band, but different countries have not been able to free the whole band. In a specific country or part of a country, for instance part of the band may be occupied by a sensitive TV link. The fixed stations in this country can easily be programmed not to use that part of the band. But roaming portables must be prohibited to transmit in that part.
Thus there is a need for recognition of channels used by a wanted system.